Eh, without the suit, T'Challa is still Captain America-durable, and the best we've seen from Danny's Iron Fist is. . . still not *that* good. Plus, T'challa isn't going to stand there and let Danny punch him, and T'Challa is faster anyway.
Basically, even without the suit, this basically goes "T'Challa hits Danny, Danny hits the ground". I mean, it might take more than one hit, but that is zero obstacle.